Existentialism is a broad concept associated with a historical movement, a philosophy and a style or mood of life. But to identify existentialism as a strict, technical philosophy is not quite right.
That is to say, it's more in line with continental philosophy than analytical philosophy, and thus has more of a distinction as an approach to life.
At the Existentialist Cafe by Sarah Bakewell:
https://www.amazon.com/Existentialist...